Method of forming silicon oxide containing films

ABSTRACT

A method of forming a silicon oxide film, comprising the steps of:
         providing a substrate into a reaction chamber;   injecting into the reaction chamber at least one silicon containing compound where the at least one silicon containing compound is bis(diethylamino)silane;   injecting Oxygen into the reaction chamber and at least one other O-containing gas selected from ozone and water;   reacting in the reaction chamber by chemical vapor deposition at a temperature below 400 C the at least one silicon containing compound and the at least one oxygen containing gas in order to obtain the silicon oxide film deposited onto the substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. application Ser. No.11/908,707, filed Mar. 17, 2006, which is a 371 of International PCTApplication PCT/EP2006/060829, filed Mar. 17, 2006, which claimspriority to JP Application No. 2005-007608, filed Mar. 17, 2005, theentire contents of each being incorporated herein by reference.

BACKGROUND

The invention relates to a method of forming silicon oxide containingfilms using a silicon precursor and an oxidant gas.

In the front end manufacture of CMOS semi-conductor devices, apassivation film such as SiN is formed on the gate electrode of each MOStransistor. This SiN film deposited on top and on side surface of thegate electrodes (such as polycrystalline silicon or metallic layers) inorder to increase the breakdown voltage of each transistor.

Attempts have been made to reduce the temperature deposition of suchSiN, to reach a temperature which is not higher than 400° C.

However, SiN films deposited at temperatures below 400° C. have usuallypoorer film qualities. In order to overcome this issue, it has beenproposed to use SiO₂ films to reinforce SiN film properties (“dualspacer”) and thereby make effective electrical barrier layers to improvesignificantly the device performances. Also, SiO₂ films are used as STI(shallow trench insulation), inter layer dielectric (ILD) layers,passivation layers, etch-stop layers and attempts are made to find adeposition process of these SiO₂ layers at low temperature, i.e. below400° C. In the specific case of dual spacer applications, the depositionof a very (20-50 A thick) thin films performed at low depositiontemperatures (300° C. at the most), should not lead to the oxidation ofthe metal electrode and should be perfectly uniform all along the gate,and an atomic layer deposition process is the most suitable such arequirement. As far as the STI applications are concerned, conformalfilms should be deposited with high deposition rate (several hundred Aper minute) below 500° C.

Deposition of silicon oxide films made from silane and oxygen at lowtemperature using a PECVD reactor have failed up to now for theseapplications, due to the incorporation of Si—H bonds into the SiO_(x)film thereby obtained, which may originate with the presence of hydrogenin the silane gas introduced as a precursor gas. The Si—H bonds thenprobably readily react with an oxygen source in the environment toproduce the Si—OH bond.

The presence of such Si—OH bonds increases the risk of havingtransistors with an increased leakage current, and therefore a reducedbreakdown voltage of the related transistors.

The inventors believe that the presence of a large number of hydrogenatoms bonded to the silicon atom in the Si precursor and of oxygen oroxygen containing gas to generate the SiO₂ film, probably also generatesmoisture (H₂O) formation which then reacts with Si to make SiOH.

The inventors also believe that the silicon containing compound shallhave preferably a high purity regarding hydrogen containing residues tolimit H₂O generation, preferably it shall contain less than 100 ppm ofH₂ or H containing compounds.

SUMMARY

It is a primary object of this invention to provide a method for formingsilicon oxide films on a substrate at a temperature of 400° C. or belowwhich prevents or limits the formation of the OH bond during the SiO₂film formation.

According to the invention, there is provided a method of forming asilicon oxide containing film comprising the steps of:

-   -   a) providing a substrate into a reaction chamber,    -   b) injecting into the reaction chamber at least one silicon        containing compound selected from the group consisting of:        -   aminosilanes having the formula (R¹R²N)_(x)SiH_(4-x) wherein            R¹ and R² are independently H, C₁-C₆ linear, branched or            cyclic carbon chain and x is comprised between 1 and 4;        -   alkoxysilanes or acetoxysilane having the formula:            Si(OR¹)(OR²)(OR³)(OR⁴), or            (OR¹)(OR²)(OR³)SiSi(OR⁴)(OR⁵)(OR⁶), or            (OR¹)(OR²)(OR³)SiRSi(OR⁴)(OR⁵)(OR⁶), or            Si(0-C(=0)-R¹)(0-C(=0)-R²)(0-C(=0)-R³)(0-C(=0)-R⁴),    -   preferably tetra(acetoxy)silane Si (0-C(=0)-Me)₄        -   wherein R, R¹, R², R³, R⁴ R⁵, R⁶ are independently H, O,            C₁-C₆ linear, branched or cyclic carbon chain;        -   silanes having the formula (SiH₃)_(n)R with n comprised            between 1 and 4, R being selected from the group consisting            of H, N, O, CH₂, C₂H₄, SiH₂, SiH, Is;        -   Tetra(isocyanato)silane Si(NCO)₄;    -   c) injecting into the reaction chamber at least one oxygen        containing gas, preferably ozone and/or oxygen and/or moisture        (water);    -   d) reacting at a temperature below 500° C. into the reaction        chamber at least one of the silicon containing compounds and at        least one of the oxygen containing gases in order to obtain the        silicon oxide containing film deposited onto the substrate;    -   e) repeating steps b) to d) until the desired SiO₂ film        thickness is obtained.

Preferably, the substrate is heated in the reaction chamber after itsintroduction, preferably up to the reaction chamber temperature, priorto carrying out steps b), c), d) and/or e).

According to a preferred embodiment of the invention, at least one stepb) and/or c) is carried out by discontinued injection of at least one ofthe compounds and/or gases. For example, pulsed CVD or ALD are carriedout in the reaction chamber.

While simultaneous injection of at least one compound and at least oneoxygen containing gas may be carried out in the reaction chamber, it ispreferred to provide alternate injection in the reaction chamber of atleast one compound and at least one oxygen containing gas.

According to another embodiment, at least one compound or the at leastone oxygen containing gas is on the surface of the substrate prior tothe injection of another compound and/or at least one oxygen containinggas.

Preferably, each compound and/or oxygen containing gas injection isfollowed by the injection of a purge gas, such as an inert gas, into thereaction chamber, while more preferably compounds and/or gas injectionsare repeated until the desired SiO₂ containing film thickness isobtained. The pressure inside the reaction chamber shall be preferablybelow 100 Torr, more preferably below 2 Torr. Preferably, the H contentin the SiO₂ containing film is less than 8.10²¹ atoms/cc.

According to another embodiment, the ozone containing gas is a gasmixture comprising oxygen and ozone with a ratio O₃/O₂ below 30% vol.,preferably between 5% and 20% vol.

Preferably, the oxygen/ozone gas mixture is diluted into an inert gas,preferably nitrogen.

The silicon containing compound shall comprise less than 100 ppm of H₂and shall be preferably selected from the group consisting of:

(TSA) Trisilylamine (SiH₃)₃N

DSO Disiloxane (SiH₃)₂O

BDEAS Bis(diethylamino)silane SiH₂(NEt₂)₂

BDMAS Bis(dimethylamino)silane SiH₂(NMe₂)₂

TriDMAS Tris(dimethylamino)silane SiH(NMe₂)₃

Bis(trimethylsilylamino)silane SiH₂(NHSiMe₃)₂

TICS Tetra(isocyanato)silane Si(NCO)₄

TEAS Tetrakis(ethylamino)silane Si(NHEt)₄

TEOS Tetrakis(ethoxy)silane Si(OEt)₄

BTESE Bis(triethoxysilyl)ethane (EtO)₃Si—CH₂—CH₂—Si(OEt)₃

TAS Tetra(acetoxy)silane Si(—O—C(═O)-Me)₄

This invention also provides a method of forming silicon oxide filmsthat inhibits or prevents OH bond introduction during film formation atlow temperatures not higher than 500° C., wherein the thickness of thesilicon oxide film is easily controlled and the silicon oxide film ishighly reliable, for example, reducing the leakage current when appliedto a gate electrode side surface.

The method of the invention also provides a SiO₂ film, particularly whendeposited using the ALD process with nitrogen purge between eachinjection, has a very high conformality (i.e. the ability to deposituniform films in the top and the bottom of a trench) useful in gap-fillapplications or for capacitors electrode for DRAM, i.e. films which fillout all the cavities on a surface and provide a uniform SiO₂ layer.

PREFERRED EMBODIMENTS

The method according to the invention for forming silicon oxide films isdescribed in details herein below. It comprises:

-   -   the use of an oxygen source and an aminosilane of the general        formula (R¹R²N)_(x)SiH_(4-x), where x is comprised between 1 and        4, where R¹ and R² are independently H or a C₁-C₆ linear,        branched or cyclic carbon chain, are independently introduced in        the reactor continuously or by pulses. Preferably injected        through an ALD process.    -   Preferably the alkylaminosilane is bis(diethylamino)silane        (BDEAS), bis(dimethylamino)silane (BDMAS) or        tris(dimethylamino)silane (TriDMAS). The alkylaminosilane is        adsorbed on the surface of the substrate (at the initial stage,        this step prevents the possible oxidation of the underlying        metal electrode during the introduction of the oxygen source).        After a purge time to evacuate the aminosilane from the reactor        using an inert gas, an oxygen source, which may consist of an        oxygen/ozone gas mixture (typically: 5-20% vol. of ozone in        oxygen), oxygen, moisture and/or hydrogen peroxide (H₂O₂) or a        combination thereof, is introduced by pulses. A cycle then        consists of one pulse of the aminosilane, one pulse of purging        gas, one pulse of the oxygen containing gas, one pulse of        purging gas. The number of cycles is determined by the targeted        thickness, taking into account the deposition rate per cycle        obtained at given experimental conditions. The deposition        temperature can be as low as room temperature and up to 500° C.,        with an operating pressure of 0.1-100 Torr (13 to 13300 Pa).        High quality films, with very low carbon and hydrogen contents,        are preferably deposited between 200 and 400° C. at a pressure        between 0.1-10 Torr (13 to 1330 Pa).    -   the use of an oxygen source and an alkoxysilane or acetoxysilane        having the formula        Si(OR¹)(OR²)(OR³)(OR⁴), or        (OR¹)(OR²)(OR³)SiSi(OR⁴)(OR⁵)(OR⁶), or,        (OR¹)(OR²)(OR³)SiRSi(OR⁴)(OR⁵)(OR⁶), or        Si(0-C(=0)-R¹)(0-C(=0)-R²)(0-C(=0)-R³)(0-C(=0)-R⁴),    -   preferably tetra(acetoxy)silane Si(0-C(=0)-Me)₄        -   wherein R, R¹, R², R³, R⁴ R⁵, R⁶ are independently H, O,            C₁-C₆ linear, branched or cyclic carbon chain, are            independently introduced in the reactor continuously or by            pulses. Preferably injected through an ALD process.            Preferably the alkoxysilane is (EtO)₃Si—CH₂—CH₂—Si(OEt)₃            (BTESE). The alkoxysilane is adsorbed on the surface of the            substrate (at the initial stage, this step prevents the            possible oxidation of the underlying metal electrode during            the introduction of the oxygen source). After a purge time            to evacuate the aminosilane from the reactor using an inert            gas, an oxygen source, which may consist of an oxygen/ozone            gas mixture (typically: 5-20% vol. of ozone in oxygen),            oxygen, moisture and/or hydrogen peroxide (H₂O₂) or a            combination thereof, is introduced by pulses. A cycle then            consists of one pulse of the alkoxysilane, one pulse of            purging gas, one pulse of the oxygen containing gas, one            pulse of purging gas. The number of cycles is determined by            the targeted thickness, taking into account the deposition            rate per cycle obtained at given experimental conditions.            The deposition temperature can be as low as room temperature            and up to 500° C., with an operating pressure of 0.1-100            Torr (13 to 13300 Pa). High quality films, with very low            carbon and hydrogen contents, are preferably deposited            between 200 and 400° C. at a pressure between 0.1-10 Torr            (13 to 1330 Pa).    -   the use of an oxygen source and tetra(isocyanato)silane having        the formula Si(NCO)₄, are independently introduced in the        reactor continuously or by pulses. Preferably injected through        an pulse-CVD process. The isocyanatosilane is adsorbed on the        surface of the substrate (at the initial stage, this step        prevents the possible oxidation of the underlying metal        electrode during the introduction of the oxygen source). After a        purge time to evacuate the silane compound from the reactor        using an inert gas, an oxygen source, which may consist of an        oxygen/ozone gas mixture (typically: 5-20% vol. of ozone in        oxygen), oxygen, moisture and/or hydrogen peroxide (H₂O₂) or a        combination thereof, is introduced by pulses. A cycle then        consists of one pulse of the isocyanatosilane, one pulse of        purging gas, one pulse of the oxygen containing gas, one pulse        of purging gas. The number of cycles is determined by the        targeted thickness, taking into account the deposition rate per        cycle obtained at given experimental conditions. The deposition        temperature can be as low as room temperature and up to 500° C.,        with an operating pressure of 0.1-100 Torr (13 to 13300 Pa).        High quality films, with very low carbon and hydrogen contents,        are preferably deposited between 200 and 400° C. at a pressure        between 0.1-10 Torr (13 to 1330 Pa).    -   the use of an oxygen source, silane (silane, disilane,        trisilane, trisilylamine) of the general formula (SiH₃)_(x)R        where x may vary from 1 to 4 and wherein R is selected from the        comprising H, N, O, CH₂, CH₂—CH₂, SiH₂, SiH, Si with the        possible use of a catalyst in ALD regime. Preferably the silane        is a C-free silane. Most preferably, the silane is        trisilylamine. A very small amount (<1%) of catalyst may be        introduced into the reactor. The silanes described above are        difficult to use in ALD conditions, as their adsorption on a        silicon wafer is not favorable. The use of a catalyst helps the        adsorption of silane on the substrate or the underlying layer.        After a purge cycle time to evacuate the silane from the reactor        using an inert gas, an oxygen source, which can consist of an        oxygen/ozone gas mixture (typically: 5-20% vol. of ozone in        oxygen), oxygen, moisture and/or hydrogen peroxide (H₂O₂) and        any combination thereof, is introduced by pulses. A cycle then        consists of one pulse of the catalyst, one pulse of purging gas,        one pulse of a silane, one pulse of purging gas, one pulse of        the oxygen source, one more purging time. Possibly, the        introduction of the catalyst is done simultaneously with the        silane, hence reducing the number of steps during the cycle, and        then its duration. The catalyst is an amine or a        metal-containing molecule, preferably a molecule containing an        early transition metal, most preferably a hafnium-containing        molecule, such as Hf(NEt₂)₄. For some applications, the catalyst        shall be C-free. The use of halides or nitrates is therefore        suggested, for instance HfCl₄ or Hf(NO₃)₄. The number of cycles        is determined by the targeted thickness, taking into account the        deposition rate per cycle obtained at given experimental        conditions. The deposition temperature can be as low as room        temperature and up to 400° C., with an operating pressure of        0.1-100 Torr. High quality films, with very low carbon and        hydrogen contents, are preferably deposited at temperature        between 2001500° C., and at pressures between 0.1-10 Torr.

Preferably, the method according to the invention is carried out asfollows:

After a substrate has been introduced into a reaction chamber, the gaswithin the chamber is first purged by feeding an inert gas into thereaction chamber under reduced pressure at a substrate temperature of 50to 400° C. Then, while at the same temperature and under reducedpressure, a pulse of a gaseous silicon compound is delivered into thereaction chamber and a very thin layer of this silicon compound isformed on the treatment substrate by adsorption. This is followed byfeeding an inert gas into the reaction chamber in order to purgetherefrom unreacted (unadsorbed) silicon compound, after which a pulseof oxygen-containing gas is delivered into the reaction chamber. Theozone-containing gas oxidizes the very thin layer of silicon compoundadsorbed on the substrate, thereby forming a very thin layer of siliconoxide and inert gas is injected into the reaction chamber to purgeunreacted products. A silicon oxide film is formed on to the substrateat the desired thickness, by repeating this sequence of inert gas purge,gaseous silicon compound pulse, inert gas purge, and oxygen-containingmixed gas pulse.

Preferably, the substrate shall be a silicon wafer (or SOI) used for themanufacture of semiconductor devices, or layers deposited thereon, or aglass substrate used for the manufacture of liquid crystal displaydevices, or layers deposited thereon. A semiconductor substrate on whicha gate electrode has been formed is used as the substrate in particularwhen the silicon oxide film is used for the purpose of improving thegate breakdown voltage.

The reduced pressure in the chamber is preferably comprised between 0.1to 1000 torr (13 to 1330 kPa) and more preferably 1 to 10 torr (133 to1330 kPa).

The reduced pressure in the chamber is preferably comprised between 0.1to 1000 torr (13 to 1330 kPa) and more preferably 1 to 10 torr (133 to1330 Pa).

The substrate temperature shall be preferably at least 50° C. and atmost 500° C., more preferably comprised between 200 and 400° C., while250 to 350° C. is even more preferred.

The inert gas used with the method of the invention shall be preferablynitrogen, argon and/or helium.

The aforementioned silicon compound can be exemplified by siliconhydrides such as silane [SiH₄], disilane [(SiH₃)₂], trisilane[(SiH₃)₂SiH₂], alkylsilane [(SiH₃)_(n)R where R represents C₁ to C₆straight-chain, branched, or cyclic alkane], trisilylamine [(SiH₃)₃N],and disiloxane [(SiH₃)₂O]; silicon alkoxides such as TEOS [Si(OC₂H₅)₄],TMOS [Si(OCH₃)₄], bistriethoxysilylethane, and trialkylsilylalkane[(RO)₃Si-Alk-Si(OR)₃ where R is C₁ to C₆ alkane], isocyanatosilaneSi(NCO)₄, acetoxysilane (Si(—O—C(═O)—CH₃)₄ and BDEAS (SiH₂(NEt₂)₂)

The silicon compound is preferably pulsed into the reaction chamberfrom, for example, a cylinder when it is gaseous at ambient temperature.When the silicon compound is a liquid at ambient temperature, as in thecase of TEOS, it can be pulsed into the chamber using a bubblertechnique. Specifically, a solution of the silicon compound is placed ina container, heated as needed, entrained in an inert gas (for example,nitrogen, argon, helium) by bubbling the inert gas therethrough using aninert gas bubbler tube placed in the container, and is introduced intothe chamber. A combination of a liquid mass flow controller and avaporizer can also be used.

The oxygen-containing mixed gas oxidizes the silicon compound andconverts it into silicon oxide. This mixed gas can be exemplified by amixed gas of ozone and oxygen and by a mixed gas of ozone plus oxygenplus an inert gas such as nitrogen, argon, or helium. The ozoneconcentration in this mixed gas is preferably 0.1 to 20% vol. An ozoneconcentration less than 0.1% vol. creates the likelihood of problemswith effecting a thorough oxidation of the monoatomic layer of thesilicon compound at low temperatures. An ozone concentration above 20%,on the other hand, creates the likelihood of problems with handling dueto the associated toxicity, instability and hazardousness of ozone.

A pulse of gaseous silicon compound can be delivered into the reactionchamber, for example, for 0.1 to 10 seconds at a flow rate of 1.0 to 100sccm. The pulse of oxygen-containing gas can be delivered into thereaction chamber, for example, for 0.1 to 10 seconds at a flow rate of10 to 1000 sccm.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in details with reference to thefollowing drawings.

FIG. 1 is a schematic diagram of a film-forming apparatus used in afilm-forming method according to an embodiment of the invention (duringan inert gas purge injection).

FIG. 2 is a schematic diagram of the film-forming apparatus of FIG. 1,during an Si compound gas injection.

FIG. 3 is a schematic diagram of the film-forming apparatus of FIG. 1during the injection of an ozone/oxygen gas pulse.

FIG. 4 is a view a metal gate of a MOS transistor with SiO₂ filmsdeposited according to the invention.

On FIG. 1, the film-forming apparatus is provided with a reactionchamber 11; a nitrogen gas cylinder 12, which is a source of an inertgas feed (for example, nitrogen gas); an Si compound gas cylinder 13,which is a source of a feed of gaseous Si compound; and an oxygencylinder 14, which is a source of an oxygen gas feed. In the case of asingle-wafer apparatus, a susceptor (not shown) is disposed within thereaction chamber 11 and one semiconductor substrate (not shown), forexample, a silicon substrate, is mounted thereon. A heater is providedwithin the susceptor in order to heat the semiconductor substrate to thespecified reaction temperature. In the case of a batch-type apparatus,from 5 to 200 semiconductor substrates are held within the reactionchamber 11. The heater in a batch-type apparatus may have a differentstructure from the heater in a single-wafer apparatus.

The nitrogen gas cylinder 12 is connected through a line L1 to thereaction chamber 11. A shutoff valve V1 and a flow rate controller, forexample, a mass flow controller MFC1, are provided in the line L1 in theorder given considered from the upstream side. A shutoff valve V2 isalso provided in the line L1 in the vicinity of the reaction chamber 11.

An exhaust line L2 that extends to a vacuum pump PMP is provided at thebottom of the reaction chamber 11. A pressure gauge PG1, a butterflyvalve BV for backpressure control, and a shutoff valve V3 are providedin the line L2 in the order given considered from the upstream side. Thevacuum pump PMP is connected through a line L3 to a detoxificationapparatus 15. This detoxification apparatus 15 can be, for example, acombustion-type detoxification apparatus or a dry-type detoxificationapparatus, in correspondence to the gas species and levels thereof.

The Si compound gas cylinder 13 is connected through a line L4 to theline L1 upstream from the shutoff valve V2 (between the shutoff valve V2and the mass flow controller MFC1). A shutoff valve V4, a mass flowcontroller MFC2, a pressure gauge PG2, and a shutoff valve V5 aredisposed in the line L4 in the order given considered from the upstreamside. The line L4 branches upstream from the pressure gauge PG2 and theresulting branch line L4′ is connected to the exhaust line L2 upstreamfrom the vacuum pump PMP (between the vacuum pump PMP and the shutoffvalve V3). A shutoff valve V5′ is provided in the branch line L4′. Thestates of the shutoff valves V5 and V5′ are synchronized in such amanner that when one is open the other is closed.

The oxygen cylinder 14 is provided with a line L5 that extends to anozone generator 16; this line L5 is provided with a shutoff valve V6 anda mass flow controller MFC3 in the order given considered from theupstream side. The ozone generator 16 is connected through a line L6with the line L1 upstream from the shutoff valve V2 (between the shutoffvalve V2 and the mass flow controller MFC1). An ozone concentrationsensor OCS, a pressure gauge PG3, and a shutoff valve V7 are provided inthe line L6 in the order given considered from the upstream side. Theline L6 is also branched upstream from the pressure gauge PG3, and theresulting branch line L6′ is connected to the exhaust line L2 upstreamfrom the vacuum pump PMP (between the vacuum pump PMP and the shutoffvalve V3). A shutoff valve V7′ is provided in the branch line L6′. Thestates of the shutoff valves V7 and V7′ are synchronized in such amanner that when one is open the other is closed.

A mixed gas of oxygen and ozone produced by the ozone generator 16 flowsinto the line L6. At a constant oxygen gas feed flow rate, control ofthe ozone concentration in the mixed gas depends mainly on pressure andthe power applied to the ozone generator 16. As a consequence, the ozoneconcentration is controlled by measuring the ozone level with an ozoneconcentration sensor OCS disposed in the line L6 and subjecting theapplied power and vessel pressure of the ozone generator 16 to feedbackcontrol based on this measured value.

An embodiment of the method for forming silicon oxide films is describedhereinbelow using the film-forming apparatus described on FIGS. 1 to 3.

1) Nitrogen Gas Purge

A treatment substrate, for example, a semiconductor wafer (not shown),is mounted on the susceptor within the reaction chamber 11 and the waferis heated to 50 to 400° C. by a temperature regulator incorporated inthe susceptor. As shown in FIG. 1, the shutoff valves V5 and V7 areclosed and the other shutoff valves V1 to V4, V6, V5′, and V7′ are allopen. The closed control valves are shown filled in black in FIG. 1,while the open control valves are shown in white. The status of theshutoff valves in the following description is shown in the same manner.

Then, while exhausting the gas within the reaction chamber 11 throughthe exhaust line L2 by the operation of the vacuum pump PMP, nitrogengas is introduced from the nitrogen gas cylinder 12 through the line L1and into the reaction chamber 11 under feed flow rate control by themass flow controller MFC1. A nitrogen gas purge is thereby carried outat a desired vacuum (for example, 0.1 to 1000 torr) by exhausting thegas within the reaction chamber 11 and feeding nitrogen gas into thereaction chamber 11 and the interior of the reaction chamber 11 issubstituted by nitrogen gas.

Beginning with and continuing from the above-described nitrogen gaspurge step, Si compound gas is continuously fed into the line L4 fromthe Si compound gas cylinder 13 under feed flow rate control by the massflow controller MFC2. However, during the nitrogen gas purge stepdescribed above, the shutoff valve V5, which resides in the line L4 thatconnects to the line L1 that extends to the reaction chamber 11, isclosed and the shutoff valve V5′, which resides in the branch line L4′that connects to the exhaust line L2, is open, and as a result this Sicompound gas is not fed into the reaction chamber 11 during the nitrogengas purge step, but rather is exhausted by feed through the lines L4 andL4′ into the exhaust line L2.

In addition, beginning with and continuing from the above-describednitrogen gas purge step, oxygen gas is continuously fed through the lineL5 from the oxygen gas cylinder 14 to the ozone generator 16 under feedflow rate control by the mass flow controller MFC3. A desired powerlevel is applied to the ozone generator 16, and oxygen containing ozoneat a desired concentration (the mixed gas) is fed into the line L6 fromthe ozone generator 16 while measuring the ozone level with the ozoneconcentration sensor OCS provided in the line L6, through which themixed gas of ozone and oxygen flows, and exercising feedback control ofthe applied power and the vessel pressure of the ozone generator 16based on the resulting measured value. However, during the nitrogen gaspurge step described above, the shutoff valve V7, which resides in theline L6 that connects to the line L1 that extends to the reactionchamber 11, is closed and the shutoff valve V7′, which resides in thebranch line L6′ that connects to the exhaust line L2, is open, and as aresult this ozone+oxygen mixed gas is not fed into the reaction chamber11 during the nitrogen gas purge step, but rather is exhausted by feedthrough the lines L6 and L6′ into the exhaust line L2.

2) Si Compound Gas Pulse

Proceeding from the state shown in FIG. 1, the shutoff valve V5′ in thebranch line L4′ is closed and, in synchrony with this operation, theshutoff valve V5 in the line L4 is opened, as shown in FIG. 2. After adesired period of time, the status of each of these shutoff valves V5and V5′ is then reversed. During the interval in which the shutoff valveV5 is open, Si compound gas from the Si compound gas cylinder 13 is fedunder flow rate control from the line L4 into the line L1 and is pulsedinto the reaction chamber 11 along with nitrogen gas. This pulse resultsin the adsorption of an approximately monomolecular layer of the Sicompound on the heated surface of the semiconductor wafer mounted on thesusceptor in the reaction chamber 11.

3) Nitrogen Gas Purge

After the Si compound gas pulse has been delivered, a nitrogen gas purgeis carried out as in FIG. 1 by reversing the status of the shutoffvalves V5 and V5′ in the line L4 and the branch line L4′ from the statusin FIG. 2. When this is done, the unreacted Si compound remaining in thereaction chamber 11 is exhausted by means of the nitrogen gas and theinterior of the reaction chamber 11 is again substituted by nitrogengas.

4) Ozone+Oxygen Mixed Gas Pulse

Proceeding from the state shown in FIG. 1, the shutoff valve V7′ in thebranch line L6′ is closed and, in synchrony with this operation, theshutoff valve V7 in the line L6 is opened, as shown in FIG. 3. After adesired period of time, the status of each of these shutoff valves V7and V7′ is then reversed. During the interval in which the shutoff valveV7 is open, the mixed gas of ozone and oxygen, supra, is fed from theline L6 into the line L1 and is pulsed into the reaction chamber 11along with nitrogen gas. As a result of this pulse, the Si compoundadsorbed on the heated surface of the semiconductor wafer mounted on thesusceptor in the reaction chamber 11 is oxidized by the ozone+oxygenmixed gas, resulting in the formation on the surface of thesemiconductor wafer of a silicon oxide film in the form of anapproximately monomolecular layer.

A silicon oxide film of desired thickness is formed on the surface ofthe semiconductor wafer by repeating these steps of 1) nitrogen gaspurge, 2) Si compound gas pulse, 3) nitrogen gas purge, and 4)ozone+oxygen mixed gas pulse. After 4) delivery of the ozone+oxygenmixed gas pulse, a nitrogen gas purge is carried out as in FIG. 1 byreversing the status of the shutoff valves V7 and V7′ in the line L6 andthe branch line L6′ from the status in FIG. 3. When this is done,reaction by-products and the unreacted ozone+oxygen mixed gas remainingin the reaction chamber 11 are exhausted by means of the nitrogen gasand the interior of the reaction chamber 11 is again substituted bynitrogen gas.

An Si compound that is gaseous at ambient temperature is used as anexample of the gaseous Si compound in silicon oxide film formation usingthe film-forming apparatus shown in FIGS. 1 to 3 and described above.However, when an Si compound is used that is liquid at ambienttemperature, such as TEOS, gaseous Si compound can still be introducedinto the reaction chamber 11 using a bubbler procedure. In specificterms, a bubbler is provided in place of the Si compound gas cylinder 13shown in FIGS. 1 to 3 and this bubbler is connected to a branch linebranched off upstream from the valve V1 in the nitrogen gas-carryingline L1, making it possible to repeat the steps of 1) nitrogen gaspurge, 2) Si compound gas pulse, 3) nitrogen gas purge, and 4)ozone+oxygen mixed gas pulse.

One reactant can be introduced continuously while the other can beintroduced by pulses (pulsed-CVD regime).

In accordance with the preceding embodiment, by inducing the adsorption,through the delivery of a pulse of Si compound gas, of an approximatelymonomolecular layer of Si compound on the surface of the treatmentsubstrate heated to a relatively low temperature no greater than 400° C.and then, after an inert gas (for example, nitrogen gas) purge,delivering a pulse of ozone-containing mixed gas (for example, anozone+oxygen mixed gas), the thorough oxidation of the Si compoundadsorbed on the surface of the treatment substrate by the strongoxidizing action of the ozone in the mixed gas enables the formation ofa silicon oxide film in the form of an approximately monomolecularlayer. In addition, the implementation of an inert gas (for example,nitrogen gas) purge after the oxidation reaction makes it possible toprevent the adsorption of moisture within the reaction chamber by thesilicon oxide film that has been formed. This enables the formation ofan excellent silicon oxide film for which OH bond introduction has beeninhibited or prevented. Such a silicon oxide film has, for example, anexcellent performance with regard to low leakage current.

Moreover, since the Si compound adsorbed on the surface of the treatmentsubstrate is oxidized by a pulse of a mixed gas containing a suitableamount of ozone (for example, a concentration of 5 to 20%), oxidation tothe surface of the treatment substrate, which has been confirmed for theuse of ozone-containing mixed gas by CVD methods, can be prevented.There is little effect on the treatment substrate since the requiredamount of this ozone-containing mixed gas is introduced as a pulse atlow temperatures. This makes it possible to submit a treatment substratebearing a film intolerant to high temperatures or an easily oxidizablemetal film or metal silicide film to formation of a silicon oxide filmaccording to the embodiment.

On FIG. 4 is illustrated a side view of a MOS transistor comprising aSiO₂ layer according to the invention. On the wafer 100, above therespective drain 105 and source 106 is located the gate 101 in the gatedielectric material with the metal electrode 102 deposited above 101.Protective silicon oxide films 103 are laterally placed on the lateralends of the gate 101 and metal gate electrode 102.

SiO₂ films 103 are also deposited on the top of the source 106 and thedrain 105.

Examples of the invention are described below with reference to theFIGS. 1 to 4:

EXAMPLE 1

The film-forming apparatus shown in the hereinabove-described FIGS. 1 to3 was used. A silicon wafer was positioned on the susceptor in thereaction chamber 11 and the wafer was heated to 100° C. A silicon oxidefilm was formed by repeating the steps of 1) nitrogen gas purge, 2) Sicompound gas pulse, 3) nitrogen gas purge, and 4) ozone+oxygen mixed gaspulse according to the hereinabove-described embodiment using theconditions described below.

1) Nitrogen Gas Purge

-   -   pressure within the reaction chamber: 3 torr    -   nitrogen gas feed flow rate: 130 sccm    -   nitrogen gas purge time: 6 seconds        2) Si Compound Gas Pulse    -   pressure within the reaction chamber: 3 torr    -   Si compound gas: trisilylamine (TSA) gas    -   TSA gas feed flow rate: 2 sccm    -   TSA pulse time: 1 second        3) Nitrogen Gas Purge    -   pressure within the reaction chamber: 3 torr    -   nitrogen gas feed flow rate: 130 sccm    -   nitrogen gas purge time: 6 seconds        4) Ozone+Oxygen Mixed Gas Pulse    -   pressure within the reaction chamber: 3 torr    -   feed flow rate of the ozone+oxygen mixed gas (5% ozone conc.):        20 sccm    -   mixed gas pulse time: 2 seconds

EXAMPLE 2

A silicon oxide film was formed by the same method as in Example 1, butin this case heating the silicon wafer placed on the susceptor withinthe reaction chamber 11 to 200° C.

EXAMPLE 3

A silicon oxide film was formed by the same method as in Example 1, butin this case heating the silicon wafer placed on the susceptor withinthe reaction chamber 11 to 300° C.

The thickness of the silicon oxide film was measured at each cycle ofthe instant film-forming procedure in Examples 1 to 3 (Example 1 wascarried through 50 cycles). A silicon oxide film could be formed inExamples 1 to 3 with good thickness control without an incubation periodat a rate of about 1.2-1.7 A/cycle.

In addition, FT-IR analysis was carried out on the silicon oxide filmproduced in Example 3 after 200 cycles (wafer temperature: 300° C.). Itwas confirmed that film production at the low temperature of 300° C.could provide an excellent silicon oxide film in which OH bondintroduction is prevented.

Using a silicon wafer bearing a molybdenum thin film on its surface asthe sample, a silicon oxide film was formed on the surface of themolybdenum thin film using the same method as in Examples 1 to 3 (100cycles). This was followed by an examination of the status of themolybdenum thin film, which formed the underlayer for the silicon oxidefilm. Oxidation of the molybdenum thin film was not observed, eventhough an ozone+oxygen mixed gas (ozone concentration=5%) was used asthe oxidizing gas.

EXAMPLE 4 ALD Deposition of SiO₂ Films Using BDEAS and Ozone

Films were successfully deposited on silicon and iridium by ALD usingBDEAS and a mixture of ozone/oxygen, using the set-up of FIGS. 1 to 3.

The chamber was a hot-wall reactor heated by conventional heater. Theozonizer produced the ozone and its concentration was approximately 150g/m³ at −0.01 MPaG. BDEAS (Bis(diethylamino)silane, SiH₂(NEt₂)₂) wasintroduced to the reaction chamber 11 by the bubbling of an inert gas(nitrogen) into the liquid aminosilane. Experimental conditions were:

7.0 sccm O₃

93 sccm O₂

BDEAS: 1 sccm [in the range of 1 to 7 sccm]

N₂: 50 sccm

Temperature ranging between 200 and 400 C

Operating pressure: 1 Torr [in the range of 0.1 to 5 Torr]

Purge and pulse times were typically set at 5 seconds each.

The number of cycles was typically set to 600 cycles.

Experiments were performed in order to determine films characteristicssuch as deposition rate, deposition temperature, film quality and filmcomposition.

SiO₂ films were obtained on Si wafer. Depositions at 200, 250, 300, 350and 400° C. were carried out. The deposited films did include neithernitrogen nor carbon according to in-depth analysis by Auger.

SiO₂ films deposited Number of cycles were varied (350, 600 and 900cycles deposition tests) and SiO₂ films deposited to check that therewas no or negligible incubation time.

Depositions on iridium were performed in order to observe the possibleoxidation of the metal electrode. The Auger profile shows a sharpinterface between ALD SiO₂ and iridium substrate, and therefore no metaloxidation was observed.

EXAMPLE 5 ALD Deposition of SiO₂ Films Using BDMAS and Ozone

Similar experiments were carried out in the same conditions as inexample 4. High quality films were obtained at a deposition rate of 0.3A/cycle at 1 Torr between 250 and 300 C.

EXAMPLE 6 ALD Deposition of SiO₂ Films Using TriDMAS and Ozone

Similar experiments were carried out in the same conditions as inexample 4. High quality films were obtained at a deposition rate of 0.2A/cycle at 1 Torr between 250 and 300 C.

EXAMPLE 7 ALD Deposition of SiO₂ Films Using TSA, Ozone and a Catalyst[Hf(NEt₂)₄]

Films were successfully deposited on silicon by ALD by alternativelyintroducing Hf(NEt₂)₄ diluted in nitrogen, N₂, TSA, N₂, and anozone/oxygen O₃/O₂ mixture (nitrogen bubbling through a mass flowcontroller into Hf(NEt₂)₄ provides a mixture of this catalyst and N₂which is alternatively introduced in a similar way into the reactor 11).

The chamber is a hot-wall tubular reactor heated by a conventionalheater. BDEAS was introduced to furnace by the bubbling of an inert gas(nitrogen) into the liquid aminosilane. Typical experimental conditionsare:

-   -   4 sccm O₃    -   96 sccm O₂    -   TSA: 1 sccm [in the range of 1 to 7 sccm]    -   N₂: 100 sccm    -   Temperature: 400 C    -   Operating pressure: 5 Torr    -   Pulse durations were typically set at 5 seconds each and pulse        duration 10 seconds    -   The number of cycles was 44 cycles.

A thin film of silicon oxide with no detectable level of hafnium wasobserved by Auger spectroscopy.

It will be understood that many additional changes in the details,materials, steps and arrangement of parts, which have been hereindescribed in order to explain the nature of the invention, may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the appended claims. Thus, the presentinvention is not intended to be limited to the specific embodiments inthe examples given above.

What is claimed is:
 1. A method of forming a silicon oxide filmcomprising the steps of: a) providing a substrate into a reactionchamber; b) injecting into the reaction chamber at least one siliconcontaining compound where the at least one silicon containing compoundis bis(diethylamino)silane; c) injecting into the reaction chamberOxygen and at least one O-containing gas selected from ozone and water;d) reacting in the reaction chamber by chemical vapor deposition at atemperature below 400 C the at least one silicon containing compound andthe oxygen and at least one oxygen containing gas in order to obtain thesilicon oxide film deposited onto the substrate.
 2. The method of claim1, wherein the silicon oxide film forms shallow trench insulation. 3.The method of claim 1, wherein the silicon oxide film forms an interlayer dielectric.
 4. The method of claim 1, wherein the silicon oxidefilm forms a passivation layer.
 5. The method of claim 1, wherein thesilicon oxide film forms an etch stop layer.
 6. The method of claim 1,wherein the silicon oxide film forms part of a dual spacer.
 7. Themethod of claim 1, wherein the temperature is below 300 C.